An empty bus pulls up at a stop and 5 people get on. At the next stop 5 people get off and twice as many people get on as at the first stop. At the third stop 10 people get off.
How many people are on the bus at this point?
One, the bus driver.
On the 1st stop, 5 people get on. On the 2nd stop, 5 people get off and 10 (twice as many as at 1st stop) people get on. On the 3rd stop, 10 people get off. So there are (5 – 5 + 10 – 10) 0 passengers left, which leaves the bus driver as the only person on board the bus.